Field of the Invention
Embodiments of the present disclosure relate to light-weight, low-density fiber cement material compositions and methods of manufacture.
Description of the Related Art
Fiber cement based building products, such as fiber cement sheets and panels, have been widely used in building construction. Efforts have been made to develop various low cost methods to reduce the density and weight of the fiber cement while maintaining desirable performance characteristics of the material. For example, low density additives, such as ceramic microspheres, have been incorporated in fiber cement. The additives are generally selected to reduce the density of the fiber cement without impairing the performance characteristics of the final product in both installation and lifetime durability and performance.
It is, however, particularly challenging to develop suitable low density additives for fiber cement building sheets or panels comprised of multiple overlaying substrate layers because of the harsh processing conditions associated with making such products. In particular, most low density additives have difficulty surviving the physical and mechanical forces imparted by the Hatschek process, which is widely used for manufacturing cellulose fibers reinforced cement sheets and panels. The low density additives selected would have to withstand the high pressure, forces, and temperature encountered through the Hatschek process.
While air entrainment is a method that can be used to reduce the density of concrete, the technique cannot be successfully and consistently applied to aeration of fiber reinforced cementitious sheets or panels for which predictable air void content and distribution are desired. In fact, numerous studies have documented the difficulties in predicting air void content of aerated uncured concrete when subject to forces or pressure. High pressure imparted on air pockets, bursting of voids by vacuum, and rupture of voids by impact forces are some of the mechanisms for air void losses in pumping aerated concrete. Thus, even though the concept of aerating concrete is known, it has not been successfully applied to producing low density fiber cement panels or sheets because of the inconsistencies in the number, distribution, and size of air voids formed by conventional air entrainment techniques. Accordingly, there is still a need for improved aeration methods and materials for manufacturing fiber reinforced panels or sheets with consistent and evenly distributed air voids.